Visual Acuity and Its Importance in life

Visual acuity refers to the sharpness and clarity of vision, measured by the ability to distinguish objects or letters at a certain distance. It's usually measured using a Snellen chart, which displays progressively smaller letters or symbols. The result is expressed as a fraction (e.g., 20/20 or 6/6), indicating the distance at which the test is performed and the distance at which the letters can be seen.

Here are some common descriptions for visual acuity:

- 20/20 (normal vision): able to see objects clearly at 20 feet that a normal eye can also see at 20 feet
- 20/100: able to see objects clearly at 20 feet that a normal eye can see at 100 feet
- 20/200: able to see objects clearly at 20 feet that a normal eye can see at 200 feet

1. Visual Acuity Prof. Dr. Jamshed Ahmed

2. Definition Visual Acuity is the clarity or sharpness of vision. (American optometric association) Visual acuity measures how sharp your vision is at a distance. It is usually tested by reading an eye chart(AAO). the ability of the visual system to discern fine distinctions in the environment as measured with printed or projected visual stimuli (Clinical Methods: The History, Physical, and Laboratory Examinations. 3rd edition).

3. What excellent visual acuity tell us Ocular media are clear Image is clearly focused on the retina Afferent visual pathway is functioning The brain has appropriately interpreted signals received

4. Some Common Causes of visual impairment and Blindness Cataract Refractive errors Corneal opacity Diabetes mellitus Age related macular degeneration Glaucoma Trachoma Onchocerciasis

5. WHO LEVELS of VISUAL IMPAIRMENT

6. Visual Pathway

7. Basis of Visual Acuity Each individual component of a letter or shape must be resolved to be identified. A letter ‘E’ viewed at the limit of resolution (20/20, 6/6) subtends 5 min of arc. E ach individual component subtending 1 min .

8. Commonly used Charts Professor Snellen developed his chart in Utrecht in 1863. The Snellen chart is accepted as the standard chart for clinical practice but it has some problems. Some letters are more legible than others; for example, ‘L’ is easier to read than ‘E’. Patients must also be literate. Modifications to avoid this include: Landholt rings illiterate E charts

9. Other Charts ETDRS logMAR chart Lea test Golovin – Sivtsev table Rosenbaum chart Jaeger chart

10. logMAR chart the  logarithm  of the minimum angle of resolution. An observer who can resolve details as small as 1 minute of visual angle scores LogMAR 0, since the  base-10  logarithm of 1 is 0; A observer who can resolve details as small as 2 minutes of visual angle (i.e., reduced acuity) scores LogMAR 0.3, since the base-10 logarithm of 2 is near-approximately 0.3; and so on.

11. Lea test

12. Golovin – Sivtsev table

13. Rosenbaum chart

14. Jaeger chart

15. Documenting Visual Acuity For Distance VAR VAL S 6/36 6/36 Ph 6/12 6/12 e 6/9 6/9 Binocular vision 6/6 6/6 For Near. N/6 N/6

16. Why visual acuity improve with Pin Hole

17. Significance of a pin hole test Refractive error/ pathology. For further investigation. When performing refraction is unnecessary or difficult. Measuring potential visual acuity post-cataract extraction. Potential acuity pinhole (PAP) is a monocular test using a pinhole occluder to view a near target amidst bright illumination to predict visual status postoperatively. The PAM test, requires additional and more costly equipment for projection. A decrease in visual acuity indicates a pathology in the visual axis.